An actuator can be formed using a material that changes shape in response to application of an external force and that returns to a predictable shape after the force is removed. One example is a shape memory alloy (SMA). SMAs typically change shape in response to the application of heat and return to the same or substantially the same shape after the heat source is removed. In many instances, an SMA will change shape in response to a current passing through the SMA (e.g. where the current passing through the SMA heats the SMA).
Previous actuators formed from SMAs have been powered by applying a DC current through the SMA element. These actuators have experienced multiple difficulties which have prevented them from being used in practice. In particular, SMAs have been difficult to actuate within a reasonable amount of time for many applications, generally taking longer than 500 ms to sufficiently heat the SMA to the point at which it actuates. To obtain faster actuation, high currents have been passed through the SMA element. While this allows for actuation speeds up to around 5 ms, the life cycle of these actuators is greatly reduced (e.g. they can be used for far less than 100 thousand cycles while maintaining adequate performance). It was generally believed that an SMA based actuator could not be created which was both responsive and had a sufficient life.